1. Field of the Invention
The invention relates in general to a method and a device for adjusting a control parameter of a servo of an optical drive, and more particularly to a method and a device that introduces a sinusoidal signal into a control loop of a servo system and then obtains the gain and/or phase variations of the introduced sinusoidal signal so as to derive required parameter regarding the control loop.
2. Description of the Related Art
FIG. 1 is a block diagram showing a servo system of a conventional optical drive. An optical sensor 102 receives an optical signal reflected from a disk (not shown) and converts the reflected optical signal into an electric signal such that a pre-stage amplifier 104 manipulates the electric signal and generates a tracking error signal Te/focusing error signal Fe. The gain and phase of the processed signal Te/Fe is then compensated into a compensator 108 after the data format of the tracking error signal Te/focusing error signal Fe is converted by an ADC (Analog to Digital Converter) 106 . After the compensated tracking error signal Te/focusing error signal Fe is processed by a DAC (Digital to Analog Converter) 110, a signal Tro/Foo is obtained and directed into a drive circuit 114 so as to derive a control signal T/F for controlling a position of an optical pickup 116. A laser diode (not shown) in the optical pickup 116 generates a laser beam to read/write the optical disk. The ADC 106, the compensator 108 and the DAC 110 may be integrated in an identical ASIC 112 as applications.
However, the physical property of the system may vary from the normal due to the temperature variation after a long-term working. That is, the gain and/or phase of the control loop formed by the drive circuit 114, the optical pickup 116, the optical sensor 102 and the pre-stage amplifier 104 may deviate from the normal situation and make the system unstable. This system instability may affect the disk-read/-write operations.
There are several solutions proposed for overcoming the aforementioned disadvantage in the conventional. Firstly, an additional temperature sensor is introduced into the optical disk system to sense the temperature variations. The gain variation of the control loop is then estimated according to the temperature variation. This approach, however, cannot obtain a precise gain variation, which indicates that the improvement to the system instability is quite relatively restricted. In addition, the extra component still increases the cost of the optical disk drive. Secondly, the read/write speed of the optical disk drive is decreased so as to reduce the read/write error rate. However, this solution cannot really solve the problem of gain/phase variations.